Bootstrap diode circuits

ABSTRACT

Bootstrap diode circuits are disclosed. Example bootstrap diode circuits disclosed herein include a first diode having a first diode input coupled to a voltage supply and a first diode output. Disclosed bootstrap diode circuits additionally include a second diode having a second diode input coupled to the first diode output and a second diode output and a plurality of zener diodes coupled in series. The plurality of series-coupled zener diodes are further coupled in parallel with the second diode.

FIELD OF THE DISCLOSURE

This disclosure relates generally to bootstrap circuits and, moreparticularly, to bootstrap diode circuits.

BACKGROUND

Gate driver circuits used to drive the gates of high-side and low-sideN-channel MOSFETS (“N-MOSFETS”) typically include a bootstrap circuit toprovide a floating power supply for the gate of the high-side N-MOSFET.The floating power supply provides a voltage level sufficient to biasthe gate of the high-side N-MOSFET relative to the source therebycausing the high-side N-MOSFET to turn on (i.e., conduct current). Insome applications, turning on the high-side N-MOSFET causes a powersupply to be coupled to a load.

Bootstrap circuits are often implemented using a capacitor that ischarged via current supplied through a bootstrap diode in series with abootstrap resistor connecting to a low-side voltage supply. When thecapacitor is sufficiently charged, the high-side N-MOSFET is turned oncausing the bootstrap diode to be subjected to a reverse bias voltagecommensurate with the magnitude of the voltage rating of the powersupply. To ensure proper operation, the bootstrap diode technology ischosen to block the reverse bias voltage. By way of example, a bootstrapdiode device used in an application having a 100 volt (V) power supplymust be able to block a reverse bias voltage of 100V.

Unfortunately, many applications require a 200V power supply or have towithstand 200V of supply surges. However, the development of newtechnology to support a single-chip gate driver integrated circuithaving a bootstrap diode rated to withstand 200V can be both costly andtime consuming. Although single-chip gate driver circuits having abootstrap diode rated for 100V are commercially available, a bootstrapdiode rated to withstand a maximum reverse bias voltage of 100V will getdamaged when exposed to a reverse bias voltage of 200V and, thus, cannotbe reliably used to operate with a 200V power supply. As a result,bootstrapping a gate driver circuit on an integrated circuit (IC) thatmay be subject to a high reverse bias voltage (e.g., >200V) typicallyrequires extra pins on the IC and components (e.g., a 200V diode)external to the IC, which raises system complexity and cost.

SUMMARY

The methods and apparatus disclosed herein relate generally to bootstrapcircuits and more particularly, to bootstrap diode circuits. Someexample bootstrap diode circuits disclosed herein are disposed on anintegrated circuit and include a first diode having a first diode inputcoupled to a voltage supply and a first diode output. Example bootstrapdiode circuits disclosed herein additionally include a second diodehaving a second diode input coupled to the first diode output and asecond diode output. Example bootstrap diodes circuits further include aplurality of zener diodes coupled in series and the series-coupled zenerdiodes are coupled in parallel with the second diode. In some examples,a first area associated with the second diode is six times greater thana second area associated with the first diode.

Some example bootstrap diode circuits disclosed herein additionallyinclude a MOSFET coupled in parallel with the first diode. In someexamples, the plurality of series-coupled zener diodes are a firstplurality of zener diodes and the bootstrap diode circuit furtherincludes a second plurality of series-coupled zener diodes. The secondplurality of zener diodes, in some examples, is coupled in parallel withthe first diode.

Further example bootstrap diode circuits disclosed herein include afirst MOSFET coupled in parallel with the first diode and a secondMOSFET coupled in parallel with the second diode. In some such examples,the first MOSFET and the second MOSFET are N-MOSFETS. In some suchexamples, the first MOSFET is an N-MOSFET and the second MOSFET is aP-MOSFET.

In some examples, the bootstrap diode circuit disclosed herein alsoincludes a voltage limiting circuit coupled between a gate terminal ofthe first MOSFET and a source terminal of the first MOSFET. In some suchexamples, the voltage limiting circuit includes a zener diode coupled inseries with a resistor.

Some example bootstrap diode circuits disclosed herein also include aboost driver circuit having a voltage sensing circuit, a comparatorcircuit and a charge pump circuit. In some such examples the voltagesensing circuit includes a first input coupled to the first output ofthe gate driver circuit and a first voltage sensing output and a secondvoltage sensing output. In some such examples, the comparator circuitdisclosed herein includes a first comparator input and a secondcomparator input coupled to the first voltage sensing output of thevoltage sensing circuit and the second voltage sensing output of thevoltage sensing circuit, respectively. The charge pump circuit includesa first charge pump input and a second charge pump input coupled to afirst comparator output and a second comparator output, respectively.The charge pump circuit also includes a first charge pump output coupledto a gate of the MOSFET.

Some example methods disclosed herein to drive a switching deviceinclude charging a charging device coupled to a switching device, andturning on the switching device by delivering charge from the chargingdevice to the switching device, to cause a reverse bias voltage to beapplied to a bootstrap diode circuit. In some such examples, thebootstrap diode circuit includes first and second diodes coupled inseries, and the first and second diodes having respective reverse biasvoltage ratings. Some such example methods also include blocking, withthe first and second diodes, the reverse bias voltage, the magnitude ofthe reverse bias voltage exceeding the respective reverse bias voltagesof the first and second diodes. The magnitude of the reverse biasvoltage can be twice as large as the reverse bias voltage rating of thefirst and second diodes. In some examples the magnitude of the reversebias voltage is equal to or less than a maximum junction voltage of anintegrated circuit on which the switching device is disposed. In someexamples, the reverse bias voltage ratings of the first and second diodeare equal.

In some example methods the second diode is coupled to an output of thebootstrap diode circuit and the reverse bias voltage is applied at theoutput of the bootstrap diode circuit. In some such example methods, afirst area associated with the first diode is six times smaller than asecond area associated with the second diode. In yet further examplemethods, the second diode is coupled to an output of the bootstrap diodecircuit, the reverse bias voltage is applied at the output of thebootstrap diode circuit, and the bootstrap diode circuit furtherincludes a plurality of zener diodes coupled in series. In some suchexample methods, the plurality of zener diodes are coupled in parallelwith the second diode and the method further includes clamping, with theplurality of zener diodes, the voltage across the second diode to amagnitude less than or equal to the reverse bias voltage rating of thesecond diode.

In further example methods disclosed herein, the switching device is afirst switching device, and the bootstrap diode circuit further includesa second switching device coupled in parallel with the first diode. Somesuch further example methods additionally include turning on the secondswitching device when charging the charging device. In some examplemethods, the switching device is a first switching device, and thebootstrap diode circuit further includes a second switching devicecoupled in parallel with the first diode, and a third switching devicecoupled in parallel with the second diode, and the example methodsfurther include turning on the second switching device and the thirdswitching device when charging the charging device.

In some examples, the bootstrap diode circuit further includes a firstplurality of zener diodes coupled in series and the first plurality ofzener diodes being coupled in parallel with the first diode. Thebootstrap diode circuit can also include a second plurality of zenerdiode coupled in series and the second plurality of zener diodes arecoupled in parallel with the second diode. In some such examples, themethod additionally includes clamping, with the first plurality of zenerdiodes, the voltage across the first diode to a magnitude less than orequal to the reverse bias voltage rating of the first diode, andclamping, with the second plurality of zener diodes, the voltage acrossthe second diode to a magnitude less than or equal to the reverse biasvoltage rating of the second diode.

In further examples disclosed herein, the switching device is a firstswitching device, and the diode circuit further includes a secondswitching device coupled in parallel with the first diode, and a thirdswitching device coupled in parallel with the second diode. In some suchexamples, the method also includes turning on the second switchingdevice and the third switching device when charging the charging device.In some such examples, the second switching device and the thirdswitching device are MOSFETS. In some examples, the second switchingdevice is an N-MOSFET and the third switching device is a P-MOSFET.

In yet other example methods, the second switching device is a MOSFETand the bootstrap diode circuit further includes a voltage limitingcircuit coupled between the gate of the MOSFET and the source of theMOSFET. The voltage limiting circuit includes a zener diode coupled inseries with a resistor. In some such examples, the method furtherincludes limiting the gate to source voltage applied to the MOSFET to athreshold value. In some examples, the bootstrap diode circuit alsoincludes a MOSFET coupled in parallel with the first diode and themethod further includes sensing a gate driver voltage at an output of agate driver circuit, comparing the gate driver voltage to a referencevoltage, and turning the MOSFET off when the gate driver voltage isdetermined to be greater than the reference voltage. In furtherexamples, the method includes determining that the gate driver voltagebecomes less than the reference voltage for a threshold amount of time,and after the threshold amount of time, turning the MOSFET on.

Example switch controllers disposed on integrated circuits are alsodisclosed herein. An example switch controller includes a switch gatedriver circuit to control first and second switches, and a bootstrapcircuit coupled to the gate driver circuit. The bootstrap circuitincludes a diode circuit having a first diode and a second diode coupledin series. The diode circuit is to block a reverse bias voltage having amagnitude that exceeds a first reverse bias voltage rating of the firstdiode and that exceeds a second reverse bias voltage rating of thesecond diode. In some examples, the magnitude of the reverse biasvoltage is equal to or less than a maximum junction voltage of theintegrated circuit. In some examples, the magnitude of the reverse biasvoltage is twice as large as the first reverse bias voltage rating andthe second reverse bias voltage rating. In some examples, the reversebias voltage is applied to the output of the second diode and the areaof the second diode is six times greater than the area of the firstdiode.

In further examples, the reverse bias voltage is applied to an output ofthe second diode, and the diode circuit of the switch controller furtherincludes a plurality of series-coupled zener diodes that are coupled inparallel with the second diode. In yet further examples, the reversebias voltage is applied to an output of the second diode, and the diodecircuit of the switch controller further includes a MOSFET coupled inparallel with the first diode.

In some examples disclosed herein, the plurality of zener diodes is afirst plurality of zener diodes, and the diode circuit includes a secondplurality of zener diodes coupled in series, the second plurality ofzener diodes being coupled in parallel with the first diode. Inaddition, the example diode circuit further can include a first MOSFETcoupled in parallel with the first diode and a second MOSFET coupled inparallel with the second diode. In some such examples, the first MOSFETand the second MOSFET are N-MOSFETS. In yet further examples, the firstMOSFET is an N-MOSFET and the second MOSFET is a P-MOSFET.

In some examples disclosed herein, the diode circuit further includes afirst MOSFET coupled in parallel with the first diode, a second MOSFETcoupled in parallel with the second diode, and a voltage limitingcircuit coupled between the gate of the first MOSFET and the source ofthe first MOSFET. The example voltage limiting circuit includes a zenerdiode coupled in series with a resistor. In further examples, the diodecircuit further includes a boost driver circuit having a voltage sensingcircuit, a comparator circuit and a charge pump circuit. The voltagesensing circuit senses a gate driving voltage at an output of the gatedriver circuit and the comparator circuit compares the sensed gatedriving voltage to a reference voltage. The charge pump circuit turns onthe MOSFET coupled in parallel with the first diode based on thecomparison made by comparator circuit. Some example switch controllersdisclosed herein additionally include a level shifter to shift an inputvoltage supplied to the gate driver circuit from a first voltage levelto a second voltage level.

These and other example methods, apparatus, systems and articles ofmanufacture to implement the bootstrap diode circuit (also referred toas a diode circuit) are disclosed in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an example power conversion systemhaving an example integrated circuit on which an example gate drivercircuit and an example bootstrap diode circuit are disposed.

FIG. 2 is a schematic diagram of the example integrated circuit of FIG.1 illustrating the example gate driver circuit and the example bootstrapdiode circuit of FIG. 1.

FIG. 3 is a schematic diagram of a first example circuit to implementthe bootstrap diode circuit of FIGS. 1 and 2 having an example firstdiode in series with an example second diode.

FIG. 4 is a schematic diagram of the example bootstrap diode circuit ofFIG. 3 that further illustrates example intrinsic capacitors associatedwith the example first diode and the example second diode.

FIG. 5 is a schematic diagram of a second example circuit to implementthe bootstrap diode circuit of FIGS. 1 and 2 having an example firstdiode in series with an example second diode and also having an exampleplurality of zener diodes.

FIG. 6 is a schematic diagram of a third example circuit to implementthe bootstrap diode circuit of FIGS. 1 and 2 having an example firstdiode in series with an example second diode and also having an examplefirst plurality of zener diodes and an example second plurality of zenerdiodes.

FIG. 7 is a schematic diagram of a fourth example circuit to implementthe bootstrap diode circuit of FIGS. 1 and 2 having an example firstN-MOSFET associated with an example first intrinsic diode coupled inseries with an example second N-MOSFET associated with an example secondintrinsic diode and also having an example first and second plurality ofzener diodes.

FIG. 8 is a schematic diagram of a fifth example circuit to implementthe bootstrap diode circuit of FIGS. 1 and 2 having an example firstP-channel MOSFET (“P-MOSFET”) associated with an example first intrinsicdiode coupled in series with an example second P-MOSFET associated withan example second intrinsic diode and also having an example first andsecond plurality of zener diodes.

FIG. 9 is a schematic diagram of a sixth example circuit to implementthe bootstrap diode circuit of FIGS. 1 and 2 having an example firstdiode coupled in series with an example second diode and also having anexample plurality of zener diodes and an example N-MOSFET driven by anexample boost driver circuit.

FIG. 10 is a schematic diagram of an seventh example circuit toimplement the bootstrap diode circuit of FIGS. 1 and 2 having an examplefirst diode coupled in series with an example second diode, an examplefirst plurality of zener diodes and an example second plurality of zenerdiodes, and also having an example first N-MOSFET driven by an exampleboost driver circuit and an example second N-MOSFET.

FIG. 11 is a schematic diagram of an eighth example circuit to implementthe bootstrap diode circuit of FIGS. 1 and 2 having an example firstdiode coupled in series with an example second diode, an example firstplurality of zener diodes and a second plurality of zener diodes, anexample N-MOSFET driven by an example boost driver circuit and alsohaving an example P-MOSFET.

FIG. 12 is a schematic diagram of a ninth example circuit to implementthe bootstrap diode circuit of FIGS. 1 and 2 having an example firstdiode coupled in series with an example second diode, an example firstplurality of zener diodes, an example second plurality of zener diodes,an example N-MOSFET driven by an example boost driver circuit and alsohaving an example P-MOSFET coupled to a level shifter circuit.

FIG. 13 is a schematic diagram of an example boost driver to drive anexample N-MOSFET included in the implementations of the bootstrap diodecircuit illustrated in FIGS. 7, 9, 10, 11 and 12.

FIG. 14 is a flowchart representative of an example method which may beperformed by the example gate driver circuit of FIG. 1, the examplebootstrap diode circuit of FIGS. 1-12 and the boost driver of FIG. 13.

FIG. 15 is a flowchart representative of an example method which may beperformed by the example boost driver circuit of FIG. 13, the examplebootstrap diode circuit of FIGS. 1-12 and the boost driver of FIG. 13.

Wherever possible, the same reference numbers will be used throughoutthe drawing(s) and accompanying written description to refer to the sameor like parts, elements, etc.

DETAILED DESCRIPTION

Certain examples are shown in the above-identified figures and describedin detail below. In describing these examples, like or identicalreference numbers may be used to identify common or similar elements.The figures are not necessarily to scale and certain features andcertain views of the figures may be shown exaggerated in scale or inschematic for clarity and/or conciseness. Although the followingdiscloses example methods and apparatus, it should be noted that suchmethods and apparatus are merely illustrative and should not beconsidered as limiting. The example circuits described herein may beimplemented using discrete components, integrated circuits (ICs), or anycombination thereof.

Additionally, it is contemplated that any form of logic may be used toimplement portions of apparatus or methods herein. Logic may include,for example, circuit implementations that are made exclusively indedicated hardware (e.g., circuits, transistors, logic gates, hard-codedprocessors, programmable array logic (PAL), application-specificintegrated circuits (ASICs), etc.), exclusively in software, exclusivelyin firmware, or some combination of hardware, firmware, and/or software.Accordingly, while the following describes example methods andapparatus, persons of ordinary skill in the art will readily appreciatethat the examples are not the only way to implement such apparatus.

FIG. 1 is a block diagram representative of an example power conversionsystem 100 that down-converts an example high voltage (e.g., 200V)direct current power supply 102 to any desired voltage via an exampletransformer 104 coupled to an example load 106. An example gate drivercircuit 108 disposed on an integrated circuit controls the flow ofcurrent through an example high-side MOSFET (“MOSFET Q1”) 110 and anexample low-side MOSFET (“MOSFET Q2”) 112 to permit the supply ofvoltage from the high voltage power supply 102 to the load 106. In someexamples, an example drain terminal 114 of the MOSFET Q1 110 is coupledto the high voltage power supply 102 and an example source terminal 116of the MOSFET Q1 110 is coupled to an example drain terminal 118 of theMOSFET Q2 112 and is further coupled to an example first output (“HSoutput”) 120 of the gate driver circuit 108. An example gate terminal122 of the MOSFET Q1 110 is coupled to an example second output (“HOoutput”) 124 of the gate driver circuit 108. An example gate terminal126 of the second MOSFET Q2 112 is coupled to an example third output(“LO output”) 128 of the gate driver circuit 108 and an example sourceterminal 130 of the second MOSFET Q2 112 is coupled to ground.

An example pulse width modulation controller 132 provides necessarysignaling to an example high-side input (“HI input”) 136 of the examplegate driver circuit 108 and an example low-side input (“LI input”) 138of the gate driver circuit 108. The signals supplied by the pulse widthmodulation controller 132 to the HI input 136 and the LI input 138 areused by an example controller circuit 140 of the gate driver circuit 108to control an example high-side driver circuit 142 coupled to theexample HS output 120, the example HO output 124 and an example low-sidedriver circuit 144 coupled to the example LO output 128.

In operation, when the example HI input 136 is set to a logic high, theexample LI input 138 is set to a logic low and vice versa. Additionally,when the LI input 138 is set to a logic high, the example controller 140causes the example low-side driver circuit 144 to supply a voltage(e.g., V_(DD)=20 V) to the example LO output 128 which, in turn causesthe example gate terminal 126 of the MOSFET Q2 112 to be positivelybiased relative to the example source terminal 130 of the MOSFET Q2 112(which is coupled to ground). Positively biasing the gate terminal 126of the MOSFET Q2 112 relative to the source terminal 130 of the MOSFETQ2 112 causes the MOSFET Q2 112 to turn ON (i.e., begin conductingcurrent). In addition, when the LI input 138 is a logic high, the HIinput 136 is a logic low such that the high-side driver circuit 142drives the HS output 120 and the HO output 124 to zero volts. Becausethere is an insufficient bias voltage between the gate terminal 122 andthe source terminal 116 of the MOSFET Q1 110, the MOSFET Q1 110 isturned OFF. As a result, the high voltage power supply 102 is notcoupled to the load 106.

With the example MOSFET Q2 112 turned ON, current flows from an examplelow voltage direct current power supply VDD 134 through an examplebootstrap diode circuit 146 of the example gate driver circuit 108 to anexample output (“HB” output”) 147. The current then charges an examplebootstrap capacitive circuit 148 that is coupled to the example HSoutput 120 and that is further coupled to the example drain 118 of theMOSFET Q2 112. Provided that the example bootstrap capacitive circuit148 is charged for a sufficient duration of time, the voltage across thebootstrap capacitive circuit 148 is approximately V_(DD)−V_(DIODE),where V_(DIODE) is equal to the voltage drop across the bootstrap diodecircuit 146. Thus, when the MOSFET Q2 112 is turned ON, the MOSFET Q1110 is turned OFF, the load 106 is uncoupled from the high voltage powersupply 102, and the capacitive circuit 148 is charging.

To turn on the example MOSFET Q1 110, the example HI input 136 is set tohigh and the example controller circuit 140 responds by causing theexample high-side driver circuit 142 to supply a voltage signal to theexample output HS 120. In some examples, the levels of voltage suppliedto the example output HS 120, the example output HO 124 and the exampleoutput HB 147 are shifted up by a level shifter (described further belowwith respect to FIG. 2) to a voltage level that is commensurate with thevoltage levels generated by the high voltage power supply 102 and thatare present at the example drain terminal 114 and the example sourceterminal 116 of the MOSFET Q1 110 when the MOSFET Q1 110 is turned ON.The voltage level at the example HB output 147 is equal to the voltagelevel present at the HS output 120 plus the voltage across the examplebootstrap capacitive circuit 148 (e.g., V_(DD)−V_(DIODE)). As a resultof the difference between the voltage level at the HS output 120 and thevoltage level at the HB output 147, the voltage present at the HO output124 rises thereby biasing the example gate 122 of the MOSFET Q1 110relative to the example drain 114 of the MOSFET Q1 110 causing theMOSFET Q1 110 to turn ON. As described above, when the MOSFET Q1 110 isON, the MOSFET Q2 112 is turned OFF. Thus, current flows from the highvoltage power supply 102 through the MOSFET Q1 110 to the load 106 viathe example transformer 104. In some examples, an isolation and feedbackcircuit 150 coupled between the load 106 and the pulse width modulationcontroller 132 operates to isolate the load from the rest of thecircuitry and to reduce the effects of feedback.

An example implementation of the example gate driver circuit 108 of FIG.1 is illustrated in the example circuit diagram of FIG. 2. First examplecircuitry implementing the example controller circuit 140, secondexample circuitry implementing the example high driver circuit 142, andthird example circuitry implementing the example low driver circuit 144are depicted in FIG. 2. As illustrated in FIG. 2, the example controllercircuit 140 can include example AND gates, an example under voltagedetector, and example buffers. As also shown in FIG. 2, the example highdriver circuit 142 can include an example AND gate, an example buffer,an example voltage level shifter and an example under voltage detector.As further illustrated in FIG. 2, the example low driver circuit 144 canbe implemented using an example buffer. Example circuits to implementthe bootstrap diode circuit 146 are depicted in FIGS. 3-11 as describedbelow.

Referring again to FIG. 1, when the example MOSFET Q1 110 turns ON(i.e., begins conducting current), the magnitude of the voltageappearing at the example source 116 of the MOSFET Q1 110 is equal to themagnitude of the voltage (e.g., 200V) supplied by the high voltage powersupply 102 causing a reverse bias voltage to be present at the exampleHB output 147. The magnitude of the reverse bias voltage present at theHB output 147 is equal to the magnitude of the voltage supplied by thehigh voltage power supply 102 plus the voltage across the bootstrapcapacitor circuit 148 (V_(DD)−V_(DIODEDROP)). To effectively block thereverse bias voltage and thereby prevent diode breakdown, the bootstrapdiode circuit 146 includes circuit components that are capable ofwithstanding the reverse bias voltage on the order of 200V, as describedfurther below.

One way to ensure that the bootstrap diode circuit is able to withstandthe large reverse bias voltage is to ensure that any circuit elementscontained in the bootstrap diode circuit are rated to withstand a largereverse bias voltage. For example, single-chip gate driver circuits thatare equipped with a bootstrap diode circuit containing a fast dioderated to withstand a 100V reverse bias voltage are commerciallyavailable. However, new technology needs to be developed for themanufacture of a single-chip gate driver circuit equipped with bootstrapdiodes capable of withstanding a 200V reverse bias voltage and suchtechnology development is both costly and time consuming. Instead, whenan application requires a 200V power source, circuit designers couple anexternal fast diode rated to withstand a 200V reverse bias voltage to anintegrated chip containing a gate driver circuit. However, addingexternal components to an existing integrated chip is a complex andcostly solution that adversely impacts the size of the circuit and isgenerally not preferred.

The example bootstrap diode circuits 146 described herein includecircuit components that are configured in a manner that permits thebootstrap diode circuit to withstand a reverse bias voltage having amagnitude greater than the magnitude of the reverse bias voltage thatthe individual circuit components are rated to withstand. In someexamples, the bootstrap diode circuits described herein are capable ofwithstanding a reverse bias voltage having a magnitude that is equal toor less than a maximum junction voltage rating of the integrated circuiton which the bootstrap diode circuit and the gate driver circuit arebuilt. In some examples, as described further below, the bootstrap diodecircuits disclosed herein are capable of withstanding a reverse biasvoltage having a magnitude that is twice as large and even four times aslarge as the reverse bias voltage ratings of the individual circuitcomponents included in the bootstrap diode circuits.

As shown in FIG. 3, in some examples, the example bootstrap diodecircuit 146 of FIG. 1 includes an example first diode 302 coupled inseries with an example second diode 304. In some such examples, thefirst and second diodes 302, 304 have equal reverse bias voltage ratingsand are coupled in series. In some such examples, the first and seconddiodes have equal reverse bias voltage ratings and the area of thesecond diode is at least six times larger than the area of the seconddiode. The first diode 302 and the second diode 304 inherentlyexperience capacitive effects that are illustrated in the schematicdiagram of FIG. 4. As shown in FIG. 4, an example first intrinsiccapacitor 402 exists in parallel with the first diode 302 and an examplesecond intrinsic capacitor 404 having an example input 406 existsbetween an example output 408 of the first diode 302 and an exampleinput 410 of the second diode 304. An example third intrinsic capacitor412 exists in parallel with the second diode 304.

Due to the large capacitance represented by the second intrinsiccapacitor 404 and associated with the first diode 302, when the outputof the bootstrap diode circuit 146 is subjected to a large reverse biasvoltage, the voltage can be unevenly distributed between the first andsecond diodes 302, 304. As a result, the second diode 304 may experiencea greater portion of the reverse bias voltage. To offset this effect,the area of the second diode 304 is increased to a size sufficient toensure that the capacitance of the third intrinsic capacitor 412 isequal to the sum of the capacitances of the first and second intrinsiccapacitors 402, 404. In some such examples, the area occupied by thesecond diode 304 on the integrated circuit is six times larger than anarea occupied by the first diode 302 to achieve the desired capacitancelevels and thereby ensure that the reverse bias voltage present at theoutput of the bootstrap diode circuit 146 is equally distributed amongthe first diode and second diodes 302, 304. As illustrated in FIG. 4, insome examples, an example output 414 of the second intrinsic capacitor404 and an example input 416 to the first diode 302 are both coupled toan alternating current (“AC”) ground.

As shown in FIG. 5, in some examples, the example bootstrap diodecircuit 146 of FIG. 1 includes an example first diode 302 coupled inseries with an example second diode 304 and a plurality ofseries-coupled zener diodes 502. In some such examples, the plurality ofseries-coupled zener diodes 502 are coupled in parallel with the seconddiode 304 and operate to clamp the voltage across the second diode 304to a desired voltage level. For example, fourteen zener diodes, eachassociated with a 7V drop, will clamp the voltage drop across the seconddiode to 98V.

In some examples, the example bootstrap diode circuit 146 of FIG. 1includes an example first diode 302 coupled in series with an examplesecond diode 304 and an example first plurality of series-coupled zenerdiodes 602 and an example second plurality of series-coupled zenerdiodes 604 as illustrated in the schematic diagram of FIG. 6. In somesuch examples, the first plurality of series-coupled zener diodes 602are coupled in parallel with the first diode 302 and operate to clampthe voltage across the first diode 302 to a desired voltage level andthe second plurality of series-coupled zener diodes 604 are coupled inparallel with the second diode 304 and operate to clamp the voltageacross the second diode 304 to a desired voltage level. In suchexamples, the number and the ratings of the zener diodes included in thefirst and the second plurality of zener diodes 602, 604 are selected toclamp the voltage across the first and second diodes 302, 304respectively, to desired levels. In some examples, 14 zener diodes, eachrated for 7V, are included in each of the first plurality and the secondplurality of zener diodes 602, 604. In some such examples, the number ofzener diodes and the active areas of the zener diodes are selected in amanner that results in matched leakage current between the first diodeand the parallel combination of the second diode along with the stringof zener diodes.

In some examples, the example bootstrap diode circuit 146 of FIG. 1includes an example first N-MOSFET 702 coupled in series with an examplesecond N-MOSFET 704 as illustrated in the schematic diagram of FIG. 7.In such examples, the first N-MOSFET 702 includes an example first“intrinsic” diode 302 i and the second N-MOSFET 704 includes an examplesecond “intrinsic” diode 304 i. The first and second intrinsic diodes302 i, 304 i are not additional to the first and second N-MOSFETs 702,704 but are rather an inherent property/feature resulting from themanner in which N-MOSFETs are constructed. In some such examples, whenthe example MOSFET Q1 110 (see FIG. 1) is turned ON such that theexample capacitive circuit 148 (see FIG. 1) is being charged, a voltagelevel present at an example gate terminal 706 of the first N-MOSFET 702is positively biased relative to a voltage level present at an examplesource terminal 708 of the first N-MOSFET 702 thereby causing the firstN-MOSFET 702 to turn ON. Thus, the first N-MOSFET 702 operates as ashort circuit, such that current does not flow through the firstintrinsic diode 302 i and no voltage drop is associated with the firstintrinsic diode 302 i. In some examples, the bias voltage is supplied bya boost driver described further below in connection with FIG. 13.

In addition, an example gate terminal 710 of the example second N-MOSFET704 is tied to an example source terminal 712 of the second N-MOSFET 704using the example second intrinsic diode 304 i of the second N-MOSFET704 as the second diode. As a result, current flows through the examplesecond intrinsic diode 304 i and charges the example capacitive circuit148 (see FIG. 1) when the example MOSFET Q1 110 (see FIG. 1) is OFF andthe example MOSFET Q2 112 (see FIG. 1) is ON.

When the example MOSFET Q1 110 (see FIG. 1) turns ON, and the MOSFET Q2112 (see FIG. 1) turns OFF, a reverse bias voltage having a magnitudeapproximately equal to the voltage supplied by the high voltage powersupply 102 (see FIG. 1) minus a voltage associated with one diode drop(e.g., the voltage drop across the example second intrinsic diode 304 i)is seen across the example bootstrap diode circuit 146. In someexamples, when the MOSFET Q1 110 (see FIG. 1) turns OFF and the MOSFETQ2 112 (see FIG. 1) turns ON, the first N-MOSFET 702 is turned OFF byshorting the example gate terminal 706 of the N-MOSFET 702 and theexample source terminal 708. In some examples, the first MOSFET 702 isturned ON and OFF via the boost driver as described below in connectionwith FIG. 13.

In some examples, the bootstrap diode circuit illustrated in FIG. 7further includes an example first plurality of zener diodes 714 coupledin series and an example second plurality of zener diodes 716 coupled inseries. The first plurality of zener diodes 714 is coupled in parallelwith the first N-MOSFET 702 and first intrinsic diode 302 i and secondplurality of zener diodes 716 is coupled in parallel with the secondN-MOSFET 704 and the second intrinsic diode 304 i. In some suchexamples, the first and second pluralities of zener diodes 714, 716clamp the voltage experienced across the first intrinsic diode 302 i andthe second intrinsic diode 304 i, respectively, to a maximum voltagelevel thereby reducing the risk that either the first or the secondintrinsic diodes 302 i, 304 i experience breakdown. In some suchexamples, when the clamping voltage achieved using the first pluralityof zener diodes 714 is equal to the clamping voltage achieved using thesecond plurality of zener diodes 716, any leakage currents associatedwith the first and second N-MOSFETS 702, 704 tend to be matched therebyfurther reducing the risk of diode breakdown.

In some examples, the example bootstrap diode circuit of FIG. 1 includesan example first P-MOSFET 802 coupled in series with an example secondP-MOSFET 804 as illustrated in FIG. 8. In such examples, the firstP-MOSFET 802 includes a first “intrinsic” diode 302 and the secondP-MOSFET 804 includes a second “intrinsic” diode 304. The first andsecond intrinsic diodes 302 i, 304 i are not additional to the first andsecond P-MOSFETs 802, 804 but are rather an inherent property/featurecaused by the manner in which P-MOSFETs are constructed. An examplefirst drain 806 of the first P-MOSFET 802 is coupled to the low voltagepower supply VDD 134 (see FIG. 1) and an example first gate 808 of thefirst P-MOSFET 802 is coupled to an example first source 810 of thefirst P-MOSFET 802. An example second drain 812 of the second P-MOSFET804 is coupled to the first source 810 of the first P-MOSFET 802 and anexample second source 814 of the second P-MOSFET 804 is coupled to anexample second gate 816 of the second P-MOSFET 804. Coupling the firstgate 808 and the second gate 816 to the first source 810 and the secondsource 814, respectively, causes both the first and second P-MOSFETs802, 804 to turn OFF (i.e., operate as an open circuit). In thisconfiguration, the first and second intrinsic diodes 302 i and 304 ioperate as two stand-alone diodes in series to conduct current movingfrom the example low voltage power supply 134 to the example secondMOSFET Q2 112 (see FIG. 1) and to block a high reverse voltage presentwhen the first MOSFET Q1 (see FIG. 1) is turned ON. The second P-MOSFET804 could be turned ON when the first MOSFET Q1 110 (see FIG. 1) turnsOFF, the second MOSFET Q2 112 (see FIG. 1) turns ON, and the examplecapacitor 148 (see FIG. 1) is being charged as the voltage level at theexample output HS 120 is at ground potential. When operating in thisexample manner, any voltage drop across the second P-MOSFET 804 iseliminated because the second P-MOSFET 804 acts as a short circuit.

When the example MOSFET Q1 110 (see FIG. 1) is turned OFF and theexample MOSFET Q2 112 (see FIG. 1) is turned ON, the voltage level at anexample input 818 of the example bootstrap diode circuit 146 is equal tothe voltage level supplied by the low voltage power supply VDD 134 (seeFIG. 1) and current flows through the first intrinsic diode 302 i andthe second intrinsic diode 304 i causing a first voltage drop associatedwith the first intrinsic diode 302 i and a second voltage dropassociated with the second intrinsic diode 304 i. Thus, the voltage atan example output 820 of the bootstrap diode circuit 146 is equal to thevoltage level supplied by the low voltage power supply VDD 134 (seeFIG. 1) minus two diode voltage drops. When the MOSFET Q1 110 (seeFIG. 1) is turned ON and the MOSFET Q2 112 (see FIG. 1) is turned OFF, areverse bias voltage is delivered to the output 820 of the bootstrapdiode circuit 146. The magnitude of the reverse bias voltage is equal tothe voltage level supplied by the high voltage power supply 102 (seeFIG. 1) minus the voltage drop across the first and the second intrinsicdiodes 302 i, 304 i. Meanwhile, the magnitude of the voltage present atthe example gate 808 of the first P-MOSFET 802 is equal to the voltagelevel supplied by the high voltage power supply 102 (see FIG. 1) dividedby two plus the voltage level supplied by the low voltage power supplyVDD 134 (see FIG. 1) minus the voltage drop across the first and secondintrinsic diode 302 i, 304 i.

In some examples, the bootstrap diode circuit illustrated in FIG. 8further includes an example first plurality of zener diodes 822 coupledin series and an example second plurality of zener diodes 824 coupled inseries. The first plurality of zener diodes 822 is coupled in parallelwith the first P-MOSFET 802 and the first intrinsic diode 302 i and thesecond plurality of zener diodes 824 is coupled in parallel with thesecond P-MOSFET 804 and the second intrinsic diode 304 i. In some suchexamples, the first and second pluralities of zener diodes 822, 824clamp the voltage experienced across the first intrinsic diode 302 i andthe second intrinsic diode 304 i, respectively, to a maximum voltagelevel thereby reducing the risk that either the first and/or the secondintrinsic diodes 302 i, 304 i experience breakdown.

In some examples, the example bootstrap diode circuit of FIG. 1 includesan example first diode 302 coupled in series with an example seconddiode 304 and an example plurality of series-coupled zener diodes 902 asillustrated in the schematic diagram of FIG. 9. In some such examples,the plurality of series-coupled zener diodes 902 are coupled in parallelwith the second diode 304 and operate to clamp the voltage across thesecond diode 304 to a desired voltage level. In some such examples, anexample N-MOSFET 904 is coupled in parallel with the first diode 302 andis turned ON when the example MOSFET Q1 110 (see FIG. 1) is turned OFFand the example MOSFET Q2 112 (see FIG. 1) is turned ON by biasing avoltage level supplied at an example gate terminal 906 of the N-MOSFET904 relative to an example source terminal 908 of the N-MOSFET 904. As aresult, the first diode 302 is shunted such that there is no forwardvoltage drop across the first diode. In some examples, the bias voltageis supplied by a boost driver 910 described further below in connectionwith FIG. 13.

As shown in FIG. 10, in some examples, the example bootstrap diodecircuit 146 of FIG. 1 includes an example first diode 302 coupled inseries with an example second diode 304, an example first plurality ofseries-coupled zener diodes 1002, and an example second plurality ofseries-coupled zener diodes 1004. In some such examples, the firstplurality of series-coupled zener diodes 1002 are coupled in parallelwith the first diode 302 and operate to clamp the voltage across thefirst diode 302 to a desired voltage level and the second plurality ofseries-coupled zener diodes 1004 are coupled in parallel with the seconddiode and operate to clamp the voltage across the second diode 304 to adesired voltage level. In some such examples, a first N-MOSFET 1006 iscoupled in parallel with the first diode 302 and a second N-MOSFET 1008is coupled in parallel with the second diode 304. When the examplebootstrap capacitive circuit 148 (see FIG. 1) is being charged via thebootstrap diode circuit 146, a level of voltage supplied at an examplefirst gate terminal 1010 of the first N-MOSFET 1006 is biased relativeto a level of voltage supplied at an example first source terminal 1012of the first N-MOSFET 1006. As a result, the first N-MOSFET 1006 turnsON causing the first diode 302 to be shunted. Thus, there is no forwardvoltage drop across the first diode 302 when current is flowing throughthe bootstrap diode circuit 146 toward the bootstrap capacitive circuit148 (see FIG. 1). In some examples, the bias voltage is supplied by aboost driver 1013 described further below in connection with FIG. 13. Insome examples, an example second gate terminal 1014 of the secondN-MOSFET 1008 is coupled to an example second source 1016 of the secondN-MOSFET 1008 thereby causing the second N-MOSFET 1008 to be turned OFF(i.e., current does not flow through the second N-MOSFET 1008 but flowsthrough its associated intrinsic diode (the second intrinsic diode 304i)). The second N-MOSFET 1008 ensures a matched leakage current to thefirst N-MOSFET 1006 when the reverse bias voltage is present at theoutput of the example bootstrap diode circuit 146. In some examples, anexample voltage limiting circuit 1018 is coupled to the source terminal1012 of the first MOSFET 1006 and includes an example zener diode inseries with an example resistor. The zener diode and resistor are sizedto ensure that the difference between a voltage present at the gateterminal 1010 and a voltage present at the source terminal 1012 does notexceed a desired threshold value (e.g., 5V). Limiting the differencebetween the voltage present at the gate terminal 1010 and the sourceterminal 1012 ensures reliable operation of the first N-MOSFET 1010during ramp up and ramp down of the example low voltage power supply 134(see FIG. 1) and when other transient voltages are present due toswitching.

In some examples, the example bootstrap diode circuit 146 of FIG. 1includes an example first diode 302 coupled in series with an examplesecond diode 304, an example first plurality of series-coupled zenerdiodes 1102, and an example second plurality of series-coupled zenerdiodes 1104, as illustrated in the schematic diagram of FIG. 11. Thefirst plurality of zener diodes 1102 is coupled in parallel with thefirst diode 302 and the second plurality of zener diodes 1104 is coupledin parallel with the second diode 304. In some such examples, the firstand second pluralities of zener diodes 1102, 1104 clamp the voltageexperienced across the first diode 302 and the second diode 304,respectively, to a maximum voltage level thereby reducing the risk thateither the first and/or the second diodes 302, 304 experience breakdown.In some examples, the first diode 302 is also coupled in parallel withan example N-MOSFET 1106 and the second diode 304 is also coupled inparallel with an example P-MOSFET 1108. In some such examples, a levelof voltage supplied to an example gate terminal 1110 of the N-MOSFET1106 is biased relative to a level of voltage supplied to an examplesource terminal 1112 of the N-MOSFET 1106. As a result, the firstN-MOSFET 1106 turns ON causing the first diode 302 to be shunted. Thus,there is no forward voltage drop across the first diode 302 when currentis flowing through the bootstrap diode circuit 146 toward the examplebootstrap capacitive circuit 148 (see FIG. 1). In some examples, thebias voltage is supplied by a boost driver 1113 described further belowin connection with FIG. 13. In some examples, an example gate terminal1114 of the P-MOSFET 1108 is tied to an example source terminal 1116 ofthe P-MOSFET 1108 causing the P-MOSFET 1108 to be turned OFF while theassociated intrinsic diode (e.g., the second intrinsic diode 304 i)operates much like the second example diode 304 of FIG. 3 and/or FIG. 6,(i.e., current does not flow through the P-MOSFET 1108.)

In some examples, the example bootstrap diode circuit 146 of FIG. 1includes an example first diode 302 coupled in series with an examplesecond diode 304, an example first plurality of series-coupled zenerdiodes 1202, and an example second plurality of series-coupled zenerdiodes 1204, as illustrated in the schematic FIG. 12. The firstplurality of zener diodes 1202 is coupled in parallel with the firstdiode 302 and the second plurality of zener diodes 1204 is coupled inparallel with the second diode 304. In some such examples, the first andsecond pluralities of zener diodes 1202, 1204 clamp the voltageexperienced across the first diode 302 and the second diode 304,respectively, to a maximum voltage level thereby reducing the risk thateither the first and/or the second diodes 302, 304 experience breakdownwhen exposed to the reverse bias voltage appearing at the output 1206 ofthe bootstrap diode circuit 146. In some examples, the first diode 302is also coupled in parallel with an example N-MOSFET 1208 and the seconddiode 304 is also coupled in parallel with an example P-MOSFET 1210. Insome such examples, a level of voltage supplied to an example gateterminal 1212 of the N-MOSFET 1208 is positively biased relative to alevel of voltage supplied to an example source terminal 1214 of theN-MOSFET 1208. As a result, the N-MOSFET 1208 turns ON causing the firstdiode 302 to be shunted. Thus, there is no forward voltage drop acrossthe first diode 302 when current is flowing through the bootstrap diodecircuit 146 toward the example bootstrap capacitive circuit 148 (seeFIG. 1). In some examples, the bias voltage is supplied by a boostdriver 1215 described further below in connection with FIG. 13. In someexamples, a level of voltage supplied to an example gate terminal 1216of the P-MOSFET 1210 is negatively biased relative to a level of voltagesupplied to an example source terminal 1218 of the P-MOSFET 1210. As aresult, the P-MOSFET 1210 turns ON causing the second diode 304 to beshunted. Thus, there is no forward voltage drop across the second diode304 when current is flowing through the bootstrap diode circuit 146toward the example bootstrap capacitive circuit 148 (see FIG. 1). Alevel shifter 1220 is used to shift the bias voltage supplied to theP-MOSFET to a level commensurate with the high voltage levels seen onthe high side of the gate driver circuit 108. The level-shifter can beimplemented using integrated 200V capacitors to shift an input signalfrom low-voltage to high-voltage without the need of 200V MOSFETs.

In some examples, an example boost driver 1300 illustrated in theschematic diagram of FIG. 13 is coupled to the provide an examplebiasing voltage at an example gate terminal 1302 of an example N-MOSFET1304 coupled in a series with a first diode 302 of the bootstrap diodecircuit 146. The boost driver 1300, which is configured to be includedon the same integrated circuit as the gate driver circuit (see FIG. 1and FIG. 2) and the bootstrap diode circuit (See FIGS. 1-12), cansimilarly be used to supply power to the example gate terminal 706 ofthe example N-MOSFET 702 of FIG. 7, the example gate terminal 906 of theexample N-MOSFET 904 of FIG. 9, the example gate terminal 1010 of theexample N-MOSFET 1006 of FIG. 10, the example gate terminal 1110 of theexample N-MOSFET 1106 of FIG. 11, and/or the example gate terminal 1212of the example N-MOSFET 1208 of FIG. 12. In some examples, the boostdriver 1300 includes an example voltage transition sensor 1306, anexample comparator 1308, and an example charge pump 1310. The voltagetransition sensor 1306 is coupled to sense the voltage at the exampleoutput HB 147 (see FIG. 1) of the example gate driver 108 (see FIG. 1)and includes the circuitry depicted in FIG. 13. In some examples, thevoltage at the output HB 147 (see FIG. 1) is sensed by the voltagetransition sensor 1306 and the associated current is limited using, forexample, resistors. In some examples, the comparator 1308 is implementedusing the circuitry depicted in FIG. 13 and compares the voltage sensedat the output HB 147 (see FIG. 1) to a fixed reference voltage (e.g.,VDD 134) to determine if the voltage at the output HB 147 is high orlow. If the voltage at output HB 147 is high (e.g., a reverse biasvoltage is present at the output HB 147), the comparator 1308 quicklysends a signal to the charge pump 1310 which responds by shortingcapacitor in the charge pump 1310 to thereby turn OFF the N-MOSFET 1304.In some examples, the voltage transition sensor 1306 and the comparator1308 are configured to rapidly turn off the N-MOSFET 1304 to prevent theexample second diode 304 from experiencing breakdown that mightotherwise occur when the output HB 147 reaches 200V at a rapid slewrate. If the voltage at the output HB 147 (see FIG. 1) goes low, thecomparator 1308 includes a timer feature such that, after a desiredthreshold amount of time, the charge pump 1310 supplies a bias voltage(e.g., VDD+5V) to the gate terminal 1302 of the N-MOSFET 1304 therebycausing the gate terminal to be 5V higher than a voltage at a sourceterminal 1312 of the N-MOSFET 1304. The use of the timer featureprevents the inadvertent turn ON of the N-MOSFET 1302 due to noise orextremely fast switching. In some examples, the charge pump 1310includes the circuitry depicted in FIG. 13.

An example method 1400 that may be performed by the example gate drivercircuit 108 (see FIG. 1), the example bootstrap diode circuit 146 (seeFIGS. 1-13) and the example boost driver 1300 (see FIG. 13) isrepresented by the flowchart shown in FIG. 14. With reference to thepreceding figures and associated written descriptions, the examplemethod of FIG. 14 begins at a block 1402 at which the example lowvoltage power supply VDD 134 (see FIG. 1) charges the example capacitivecircuit 148 (see FIG. 1) via the example bootstrap diode circuit 146(see FIGS. 1-13). As described above, the charging of the capacitivecircuit 148 occurs when the example gate driver circuit 108 operates toturn an example first MOSFET Q1 110 OFF and an example second MOSFET Q2112 ON. In some examples, a switch implemented using the exampleN-MOSFET X of FIG. X is coupled in parallel with the first example diodeor the second example diode of the bootstrap diode circuit and operatesto reduce the forward voltage drop across the first and/or second diode(see block 1406). In some examples, the switch reduces the forwardvoltage drop by turning ON thereby causing the charging current tobypass the first and/or the second diode.

When the example gate driver circuit 108 drives the example output HO122 to a logic high and the example output LO 144 to a logic low, thesecond MOSFET 112 turns OFF and, provided that the capacitive circuit148 is sufficiently charged, the first MOSFET Q1 110 turns ON (see block1404). When the first MOSFET Q1 110 turns ON, a reverse bias voltageapplied at an example output HB 147 of the bootstrap diode circuit 146is blocked by the example first diode 302 (see FIG. 3) coupled in serieswith the example second diode 304 (see FIG. 3) (see block 1408). In someexamples, an example first plurality of series-coupled zener diodesand/or an example second plurality of series coupled zener diodesoperate to clamp the voltage across the first diode and/or the seconddiode (see block 1410).

An example method 1500 that may be performed by the example boost drivercircuit 1300 (see FIG. 13) is represented by the flowchart shown in FIG.15. With reference to the preceding figures and associated writtendescriptions, the example method of FIG. 15 begins at a block 1502 atwhich the example voltage transition sensor 1306 senses a voltageassociated with the output HB 147 (see FIG. 1). The voltage transitionsensor 1306 supplies the detected voltage information to the examplecomparator circuit 1308 which compares the detected voltage to areference voltage (e.g., VDD) (see block 1504). When the detectedvoltage exceeds the reference voltage (e.g., VDD), the comparatorcircuit 1308 notifies the example charge pump circuit 1310 (see FIG. 13)which responds by removing a bias voltage from the example gate 1302 ofthe switch (e.g., the example N-MOSFET) coupled in parallel with thefirst diode 302 (see block 1506). Removal of the bias voltage causes theswitch to turn OFF. When the comparator circuit 1308 determines that thedetected voltage at the output HB 147 has dropped below the referencevoltage (e.g., VDD) for a threshold amount of time (see block 1504), thecomparator circuit 1308 notifies the charge pump which responds bysupplying the bias voltage to the gate terminal 1302 of the N-MOSFETthereby causing the N-MOSFET to turn ON (see block 1508). As describedabove, when the N-MOSFET is turned on, the forward voltage drop thatwould otherwise occur across the first diode 302 (see FIG. 13) isreduced and/or eliminated. In some examples, the bias voltage is equalto the voltage supplied by the low voltage power supply VDD 134 plus 5V.

Bootstrap circuits, configured in the manner disclosed above, providemany benefits. For example, the bootstrap diode circuits describedherein can be used to block reverse bias voltages that exceed thereverse bias voltage ratings of individual diodes included in thecircuits. In some examples, the disclosed bootstrap diode circuits canblock a maximum reverse bias voltage of 200V using fast diodes rated for100 V to implement the first diode 302 (see FIG. 3) and the second diode304 (see FIG. 3). In some examples, the disclosed bootstrap diodecircuits can block a reverse bias voltage that is twice and even fourtimes larger than the reverse bias voltage rating of the first andsecond diodes. The disclosed bootstrap diode circuits can block areverse bias voltage having a magnitude that is equal to or less than amaximum junction voltage of an integrated circuit on which theassociated switching device is disposed. Additionally, the disclosedbootstrap diode circuits are configured to have a low forward voltagedrop across the bootstrap diode circuit thereby making it easier tocharge the capacitor that is used to bias the high side MOSFET.

As an additional benefit, the bootstrap diode circuits disclosed hereincan be used to switch a high voltage power supply of 200V withoutrequiring expensive fast diodes rated to withstand 200V diodes. As aresult, existing single-chip gate driver circuits having fast diodesrated to withstand 100V configured in the manners disclosed herein canbe used with applications involving high voltage power supplies on theorder of 200V without the need to couple external fast 200V diodes tothe integrated chips.

Although certain methods and apparatus have been described herein, otherimplementations are possible. The scope of coverage of this patent isnot limited to the specific examples described herein. On the contrary,this patent covers all methods and apparatus fairly falling within thescope of the invention.

What is claimed is:
 1. A bootstrap diode circuit on an integratedcircuit, the bootstrap diode circuit comprising: a first diode having: afirst diode input coupled to a voltage supply; and a first diode output;a second diode having: a second diode input coupled to the first diodeoutput; and a second diode output; a plurality of zener diodes coupledin series, the plurality of zener diodes being coupled in parallel withthe second diode; a field effect transistor (FET) coupled in parallelwith the first diode; and a boost driver circuit including: a voltagesensing circuit having: a voltage sensing input coupled to a gate drivercircuit; and a voltage sensing output; a comparator circuit having: acomparator input coupled to the voltage sensing output; and a comparatoroutput; and a charge pump circuit having: a charge pump input coupled tothe comparator output; and a charge pump output coupled to a gate of theFET.
 2. The bootstrap diode circuit of claim 1 wherein an area of thesecond diode is at least six times greater than an area of the firstdiode.
 3. The bootstrap diode circuit of claim 1 wherein the pluralityof zener diodes is a first plurality of zener diodes, and the bootstrapdiode circuit further includes a second plurality of zener diodescoupled in series, the second plurality of zener diodes being coupled inparallel with the first diode.
 4. The bootstrap diode circuit of claim 3wherein the FET is a first FET, and the bootstrap diode circuit furtherincludes a second FET coupled in parallel with the second diode.
 5. Thebootstrap diode circuit of claim 4 wherein the first FET and the secondFET are n-channel FETs.
 6. The bootstrap diode circuit of claim 4wherein the bootstrap diode circuit further includes a voltage limitingcircuit coupled between the gate of the first FET and a source of thefirst FET, the voltage limiting circuit including a zener diode coupledin series with a resistor.